Micro & Nanofluidics

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Transcript of Micro & Nanofluidics

= ρ vD η
Re<500 : laminar flow (fluid flows in parallel layers) Re>2000 : turbulent flow
ρ : fluid density v : fluid speed η : fluid viscosity D: diameter of the pipe
Iner5a: resistance of an object to any change in its moGon (to keep moving in a straight line at constant velocity, or to keep sGll)
Viscosity: fluid resistance flow (to gradual deformaGon by shear stress)
Reynolds number For non circular channels, use the hydraulic diameter to calculate the Reynolds number: D=DH
DH = d pipe diameter
DefiniGon:
Low Reynolds number prevail not only in the micro world…
B. H. Weigl, R. L. Bardell, and C. R. Cabrera, "Lab-on-a-chip for drug development", Advanced Drug Delivery Reviews 55 (3), 349 (2003).
D =100m v =10m / year = 0.3µms−1
η =1010kgm−1 s−1
ρ =103 kgm−3
Re = ρ vD η
= 3⋅10−12 <<1
Viscous terms dominate and we have laminar flow
In a laminar flow, the viscous terms dominate Image = honey flowing in a channel
Liquid and sample transport - Pressure driven flow

University of Twente – group of Albert van den Berg
r
ParGcles at the periphery travel slower than parGcles in the center. A plug of sample is therefore spread out as it travels in the tube which may lower resoluGon of a fluidics system. It can also be useful: Large parGcles are excluded from the edges and travel on average faster than small parGcles, that can be closer to the edges (hydrodynamic chromatography).
pubs.acs.org/doi/pdfplus/10.1021/ac034663l
2a
Micro and nanofluidics - Lab on a chip Micro and nanofluidics: Can be used for fundamental studies made possible thanks to the properGes of the small channels Lab on a chip: applicaGon of micro and nanofluidics- analysis and diagnosGcs oriented Advantages over tradiGonal methods: -smaller sample and reagent amount needed -faster experiments
FabricaGon – Photolithography and Soe Lithography
PDMS
Master
PDMS
Master
PDMS
Silicon Wafer or glass slide
Diffusion: becomes important in microfluidics due to the small size of the channels.

D = µkBT = kBT 6πηa
kB: Boltzmann constant=1.38064852 × 10-23 m2 kg s-2 K-1 T: temperature η: viscosity of the fluid µ: mobility of the parGcle a: parGcule radius
In one dimension



r2

Diffusion
In general in microfluidics, the flow is laminar and there is no convecGve mixing. Due to short distances, instead diffusion becomes important.
Rhodamine
Anthocyanin
OUTLET
LE TS
Diffusive mixer
The mixing of Rhodamine and anthocyanine is achieved by diffusion only (no turbulent flow)
Work on exercises 2 and 3
In general in microfluidics, the flow is laminar and there is no convecGve mixing. Due to short distances, instead diffusion becomes important.
FITC
X
The widths of the streams at the outlet are funcGons of the relaGve flow rates at the inlet channels.
OUTLET
Rcd
Rc = distance between obstacles period of array
Basic idea: streamlines consGtute potenGal trajectories. ParGcles shie streamline, and thus trajectory, as a response to a force (here steric: they “bump” into the obstacles )
DeterminisGc lateral displacement: Bumper array
CriGcal Radius:
The parGcles with R<Rc follow the flow direcGon. The parGcles with R>Rc travel through the device at an angle compared to the direcGon of the flow.
Rcd
Rc = distance between obstacles period of array
Basic idea: streamlines consGtute potenGal trajectories. ParGcles shie streamline, and thus trajectory, as a response to a force (here steric: they “bump” into the obstacles )
DeterminisGc lateral displacement: Bumper array
CriGcal Radius:
Ideal case
The parGcles with R<Rc follow the flow direcGon. The parGcles with R>Rc travel through the device at an angle compared to the direcGon of the flow.
ApplicaGon – Ultrasimple label-free sorGng of trypanosomes Trypanosoma brucei -> sleeping sickness. •Fatal (100%) disease. •Fatal (5%) treatment. àImperaGve to minimize false negaGves as well as false posiGves.
Current diagnosis relies on enrichment by ion exchange chromatography and centrifugaGon. Simpler and cheaper methods needed that are adapted to use in remote areas. Major challenge – Need to detect as low concentraGons as 100 parasites per mL.
depth 37µm
ApplicaGon – Ultra simple label-free sorGng of trypanosomes